Abstract

An interesting feature of the iron arsenides is the magnetoelastic coupling between the long
wavelength in-plane strains of the lattice and the collective spin fluctuations of the electrons near the
magnetic ordering wavevectors. We study the microscopic origin of this feature from an electronic
model with nested Fermi pockets and a nominal interaction. We find the couplings diverge with a
power-law as the system is tuned to perfect nesting, thereby implying the magnetoelasticity in these
systems is a nesting induced feature. We also elucidate how this nesting induced singularity plays
a role in triggering a spin fluctuation driven nematic instability that gives rise to the orthorhombic
phase of these materials. These results show the microscopic connection between the nesting of
the bands with the nematic and the magnetoelastic properties of the iron arsenides.